This invention relates generally to a method and apparatus for collecting data regarding geological properties of underground or undersea formations in the vicinity of a well bore under construction. More particularly, this invention relates to a method and apparatus for collecting data regarding the formations during and after drilling and constructing the well bore. In particular, the invention relates to a method and apparatus for collecting data regarding the formations sensors, actuators and generators coupled to a well casing inside the well bore. This invention also relates to a method and apparatus for relaying data collected deep in a well to the surface.
Geologists and geophysicists collect data regarding underground formations in order to predict the location of hydrocarbons such as oil and gas. Traditionally, such information is gathered during an exploration phase. In recent years, however, the art has advanced to allow the collection of geophysical and geological data as a well is being drilled.
For example, in Vertical Seismic Profiling (xe2x80x9cVSPxe2x80x9d), drilling operations are interrupted to place a series of seismic sensors at discrete depths in a borehole. A surface source releases energy that is reflected off underground geological formations. The seismic sensors in the borehole sense the reflected energy and provide signals representing reflections to the surface for analysis.
In a subsequent development, known as xe2x80x9cdrill bit seismicxe2x80x9d, seismic sensors are positioned at the surface near the borehole to sense seismic energy imparted to the earth by the drill bit during drilling. This sensed energy is used in the traditional seismic way to detect reflections from underground geological formations. Further, this technique is used to detect xe2x80x9cshadowsxe2x80x9d, or reduced seismic energy magnitude, caused by underground formations, such as gas reservoirs, between the drill bit and the surface sensors.
A greatly simplified description of those steps involved in drilling an oil well follows. A portion of the oil well is drilled using a drill string consisting of drill pipe, drill collars and drill bit. After a portion of the well has been drilled, a section of casing, or large bore pipe, is inserted into the well bore and cemented for, among other things, zonal isolation. Casing performs a number of functions, including: preventing the bore hole from caving in; preventing fluids in the bore hole from contaminating the surrounding formations; preventing the introduction of water into the surrounding formations; containing any production from the well; facilitating pressure control; providing an environment for the installation of production equipment; and providing zonal isolation.
When the casing is in place it is cemented to the formation wall. This is accomplished by pumping cement through the casing until it exits at the end of the casing through a special section of casing called a xe2x80x9ccasing shoexe2x80x9d and flows up the annulus between the casing and the wall of the well bore. The concrete is then allowed to set.
In subsequent drilling operations, the deep end of the newly cemented casing is drilled out and another section of the well bore is drilled. The process of drilling sections of the well bore followed by inserting and cementing well casing repeats until the desired well depth is reached.
As the well bore is being drilled, drilling fluids, known as xe2x80x9cmudxe2x80x9d, are pumped into the drill string. The mud travels down the drill string until it is ejected. The mud picks up cuttings and carries them to the surface. The specific gravity of the drill mud is carefully controlled so that the weight of the column of mud is (1) large enough to prevent gas or other hydrocarbons from entering the borehole from the surrounding formations; (2) without exerting so much pressure that the surrounding formations are damaged.
After each section of casing is laid and cemented in, the fracture pressure of the formation just below the end of the casing is measured. Generally, the fracture pressure of deeper formations is greater than the fracture pressure of shallower formations. The specific gravity of the drilling mud is subsequently controlled to make sure that the pressure on the formation at the end of the casing does not exceed the fracture pressure of the formation at that point. This is generally accomplished by calculations incorporating the measured specific gravity of the drilling mud and the depth of the column of drilling mud above the formation.
Downhole data are captured using xe2x80x9cwirelinexe2x80x9d techniques in which, prior to casing being laid, a tool, such as an acoustic logging tool, is lowered into the well bore and slowly retrieved, gathering data and storing it or transmitting it to the surface as the tool is being retrieved. Alternatively, measurement while drilling (xe2x80x9cMWDxe2x80x9d) or logging while drilling (xe2x80x9cLWDxe2x80x9d) tools are attached to the drill string just above the drill bit and drill collars. These generally expensive tools gather data during the drilling process and store it or transmit it to the surface.
In general, in one aspect, the invention features a casing sensor comprising a casing shoe and a sensor coupled to the casing shoe.
Implementations of the invention may include one or more of the following. The sensor may comprise a pressure sensor. The sensor pressure may comprise a pressure transducer and a transmitter coupled to the pressure transducer. The casing sensor may comprise a surface receiver coupled to the transmitter. The casing sensor may comprise a drill string through the casing shoe.
In general, in another aspect, the invention features a casing data relay comprising a downhole receiver coupled to a well casing and a transmitter coupled to the receiver.
Implementations of the invention may include one or more of the following. The casing data relay may comprise a surface receiver coupled to the transmitter. The surface receiver may be electrically or optically coupled to the transmitter. The surface receiver may be coupled to the transmitter by electromagnetic telemetry. The surface receiver may be coupled to the transmitter by a pressure transducer. The casing data relay may comprise an antenna coupled to the downhole receiver, the antenna being configured to receive electromagnetic radiation. The casing data relay may comprise one or more casing sensors coupled to the casing, wherein one or more of the one or more casing sensors are coupled to the transmitter. The casing data relay may comprise one or more drill string sensors coupled to a drill string. At least a portion of the drill string may be inserted through the casing. The drill string sensors may be coupled to the downhole receiver. One or more of the drill string sensors may be coupled to the downhole receiver through a drill string transmitter. The casing data relay may comprise drill string instruments coupled to the transmitter and a surface transmitter coupled to the downhole receiver. The casing data relay may comprise a drill string actuator. The drill string actuator may be controllable through the downhole receiver. The drill string actuator may be configured to change a position of an adjustable gauge stabilizer. The drill string actuator may be configured to change a bit nozzle size.
In general, in another aspect, the invention features a method for collecting geological data comprising sensing one or more geological parameters during drilling using one or more sensors coupled to a well casing in a well bore, collecting data from the one or more sensors and transmitting the data to the surface. Sensing may comprise sensing using one or more sensors coupled to a casing shoe, sensing using a pressure transducer on a casing shoe, sensing pressure, sensing temperature, sensing acoustic energy, sensing stress or sensing strain. The method may further comprise transmitting acoustic energy. Transmitting may comprise transmitting the data to the surface through a relay.
In general, in another aspect, the invention features a method for maintaining the integrity of a formation in the vicinity of a casing shoe comprising measuring well bore pressure in the vicinity of the casing shoe during drilling.
Implementations of the invention may include one or more of the following. The method may comprise transmitting data representing the measured well bore pressure to the surface.
In general, in another aspect, the invention features a method for positioning look ahead sensors comprising positioning acoustic sensors along a casing string.
In general, in another aspect, the invention features a method for monitoring well control events comprising monitoring pressure at two or more locations inside a casing of the well.
Implementations of the invention may include one or more of the following. Monitoring may comprise monitoring pressure at two or more locations that are longitudinally displaced along the casing. In general, in another aspect, the invention features a method for determining whether cement in a well borehole has cured comprising positioning a temperature sensor on a casing and monitoring the temperature of the cement using the temperature sensor.
Implementations of the invention may include one or more of the following. Positioning may comprise positioning the temperature sensor inside the casing or positioning the temperature sensor on the casing shoe.